There has been known a double walled low-temperature storage case having a thermally good conductive inner box and a thermally insulating outer box and having a refrigeration unit between the boxes for refrigerating the inner box and the room inside the inner box, as disclosed in Japanese Utility Model Early Publication No. Sho 60-93882 (which will be referred to as Reference 1). A refrigerator utilizing indirect refrigeration for preserving fresh vegetables is also known, as disclosed in Japanese Patent Early Publication No. Sho 62-134477 (which will be referred to as Reference 2).
Reference 1 shows a low-temperature case wherein a thermally good conductive inner box is secured inside, but spaced apart from, a thermally insulating outer box, forming a space between them for circulating cold air therethrough to refrigerate the inner box, and thus the storage room inside the inner box. The low-temperature case is provided with an evaporator of a refrigeration unit for generating cold air and a fan for circulating the cold air through the apace. Other components of the refrigeration unit are installed outside the low-temperature case.
On the other hand, the refrigerator of the Reference 2 discloses a vegetable preservation container wherein the upper opening of the container may be tightly covered with a lid which is made up of, e.g. an intermediate plastic resin layer sandwiched with outer and inner layers of fabrics. The Reference 2 also shows a lid which is composed of: a flat plate made of thermally insulating plastic such as olefin e.g. polyethylene and having a multiplicity of penetrating holes; a moiture-permeable thin film of silicon rubber glued on one surface of the flat plate; and a rubber packing made of e.g. vinyl chloride placed along the periphery of the flat plate and the film, thereby removing the dews deposited on the lid.
However, in cases when living farm products such as fresh fruits or vegetables are stored in a low-temperature case of Reference 1, the ethylene gas produced by the living farm products through their respiration remains in the refrigerating room and changes the gas composition therein and eventually promoting aging and degradation of the farm products.
On the other hand, in the case of the refrigerator of Reference 2, since the moiture-permeable film cannot adsorb the ethylene gas released from the vegetables, it presents the same problem as in the case of Reference 1, and in addition another problem of imbalance in the moisture in the refrigeration room. So long as the rate A of moisture coming into the refrigeration room through the lid exceeds the rate B of the moisture evaporating from the vegetables, there will be no problem. But if the rate A is less than the rate B, there will be dew drops from the lid into the refrigeration room to damage the vegetables and cause the bottom of the refrigeration room polluted with unsanitary sticky stains, further degrading the vegetables.